A concept of heterogeneous network was first proposed in 3GPP Rel-10 and quickly becomes a hot point of focus in the art. Mobility enhancement under the heterogeneous network is one of work items in this filed, which is intended to improve network capacity while providing seamless and stable coverage for users.
Many problems have been discussed in the mobility enhancement under the heterogeneous network, and small cell detection is one of hot points of discussion focuses in the work item of heterogeneous network mobility enhancement of 3GPP. The heterogeneous network includes a large number of small cells, e.g., a micro base station, a pico base station, a femto base station, a radio remote unit and the like, which are mainly distributed in places such as home, office, shopping center and the like. Load on a macro base station is reduced and capacity of the network is also improved by switching user equipment to small cells.
However, the introduction of the concept of heterogeneous network has also brought about many problems. For example, the current mechanism for detecting adjacent cells is to ensure mobility of user equipment (UE), without considering new disposition environment in the heterogeneous network. Further, for example, in the existing standard, the mechanism for detecting adjacent cells is based on s-Measure and measurement for Reference Signal Reception Power (RSRP) and/or Reference Signal Reception Quality (RSRQ). Because of non-uniformity of distribution of the cells in the heterogeneous network, a macro cell has a good service quality but may be very close to the small cells, and the user equipment might not be able to detect the small cells within the macro cell. Also, for example, the small cell detection strategy always needs use of measurement gaps, and for the user equipment, frequent configuration of the measurement gaps not only consumes power, but also greatly occupies available resources.
It has been noted that in the disposition of the heterogeneous network, a scene of coverage by hotspot areas is very common. In this scene, the macro cell mainly provides coverage of large areas, and the small cells, e.g., the pico cells, provide service bearer on another frequency. Therefore, it is possible to improve an index of quality of service (QoS) for users in the hotspot areas, and it is also possible to improve throughput of the whole network. However, due to the inter-frequency disposition of the small cells and non-uniformity of the coverage range, it needs to design a corresponding mechanism to ensure the user equipment can effectively switch to the small cells. In 3GPP TR 36.839, inter-frequency small cell detection includes several common types:
a) Relaxed Measurement Configuration
According to types (serving as hotspots or providing coverage) of the small cells and a speed of the user equipment, a measurement cycle is increased to reduce unnecessary measurements and the user equipment moving at a high speed is not allowed to get access to the small cells within the hotspot. This scheme reduces power consumption on the user equipment side and interference on user plane of a serving cell, but has a poor accuracy and delay in detection.
b) Proximity Based Small Cell Indication
Inter-frequency cell measurement may be triggered based on Proximity Indication, and these schemes can be classified as being based on macro base station, based on small cells or based on user equipment. The schemes based on macro base station and based on small cells made no changes on the user plane, and the biggest problem is how to improve accuracy. Further, the scheme based on small cells needs to modify X2 interface. However, the scheme based on user equipment has higher accuracy and higher feasibility, but may increase complexity on the user equipment side.
c) Small Cell Discovery Signal in Macro Layer
The base station of the small cell transmits a cell discovery signal (constituted by Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS) and system information) on an operating frequency band of the macro cell. Thus, the user equipment may consider the small cell as a common intra-frequency cell and perform normal procedures such as measurement reporting and the like. Then, the base station may immediately trigger handover of the user equipment, or may make the user equipment perform inter-frequency cell measurement. This scheme is relatively simple, but there exists a problem that interference is caused between the small cell discovery signal and a macro cell signal and that execution of the handover might incur a certain delay. Further, forward compatibility can not be ensured, and thus traditional users can not accept and execute related signaling.
Therefore, it is intended to provide a device and method in a wireless communication system so as to improve efficiency for small cell discovery, thereby providing seamless and stable network coverage for the user.